Separating headlight lens from housing (RAV4 MK1)

[Horsey McHorseface]

I've heard mentioned the oven method, of pre-heating unit, before wrestling with the mastic to attempt to separate lens. Sounds risky to me, but I think that's my only option now, if anyone can help with some failsafe advice? I tried leaving headlight unit in the sunshine for a few hours today. UV strength 7 sunshine, beating down on that black plastic housing, but lens still felt pretty stuck on.

[Doesitdrive]

YouTube answers most things, oven works.

[Horsey McHorseface]

Just checking YT videos. I’d forgotten the other safer option of a hairdryer/heatgun.

[Horsey McHorseface]

Put in fan oven, 95c for 14 mins = easy separation. I cleaned out most of the old sealant from the housing channel, whilst still warm. Still quite a bit left. Should I just leave it there, or is there an appropriate cleaner?